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Science

More Strange Bose-Einstein Condensate Behavior 135

Posted by Roblimo from the not-necessarily-faster-than-light dept.
Allen Varney writes "According to a story on EurekAlert, an arXiv preprint server paper titled 'Scattering of atoms on a Bose-Einstein Condensate' reports that atoms striking a BEC sometimes appears to leave before they enter. 'This doesn't imply a breaking of the light-speed barrier, time travel or anything overly exotic but is a property of waves being broken down into component parts and being reassembled slightly differently. [...] As an atom hits the BEC, it is absorbed into the collective state but still exists as a vibration. The vibration travels through the BEC but can escape as an atom once more. The study reinforces the similarity between atoms as waves and light as waves.' Slashdot has talked about supposed faster-than-light travel once or twice (or more) before."
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More Strange Bose-Einstein Condensate Behavior More

More Strange Bose-Einstein Condensate Behavior

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  • Already in use? (Score:5, Funny)

    by HiQ ( 159108 ) on Friday July 05, 2002 @08:49AM (#3826855)
    I think Bose-Einstein condensates are used in the making and / or broadcasting of sitcoms and movies. You're watching a movie or sitcom, and you already know what's going to happen. My guess is that you've already seen it just slightly before.

  • The question is... (Score:4, Funny)

    by f00Dave ( 251755 ) on Friday July 05, 2002 @08:51AM (#3826871) Homepage
    ... would a particle have been emitted anyway?

    Ie: Is there enough information in the 'onset' part of the wave to cause the reconstruction of a particle at the other end, similar to the other 'faster than light' story? I'm betting there is.

    While I'm ranting: Why does the dot keep posting stories about obviously-misinterpreted science news while ignoring *serious* news like the cure for 1/3 of cancers in mice from a week ago?
    • : Is there enough information in the 'onset' part of the wave to cause the reconstruction of a particle at the other end, similar to the other 'faster than light' story?

      I think what they are saying is that the particle dissapears into the BE condensate, and another particle is constructed at the other side which is essentially identical. It may or may not be the same particle. In a sort of Zen like way, it might or might not be the same thing as went in, and its meaningless to ask if it is.

      As for the faster than light bit, I guess that's how quickly the new particle appears on the other side.

      Of course, I could be way off the mark here...

      Disclaimer: IANATP (theoretical physicist)

      Michael
      • Really, elementary particles don't have any fur. You can't distinguish between them. There is no way you can say : this electron is different from that electron (exept if they are free particles and exist at the same time, occupying a different space). But inside an atom, they're not free particles, so you can't say this is electron A and this is electron B, and they interact blah blah blah ...
        • Really, elementary particles don't have any fur. You can't distinguish between them.

          Is there any serious theory that it is somehow possible to distinguish between them, even if we can not do it? e.g. if the universe is a computer simulation, each electron might have a serial number barcoded on it. Or, since we do not know the nature of a quark - if it is round or pyramidal or furry - perhaps each one indeed is slightly different.

          So, is this useless to speculate on because it is fundamentally impossible to ever arrive at an answer (like the first cause, or how the physical laws of our universe are implemented at the lower layer) if an answer even exists? Or is this known for some reason to not be the case? Or is it possible, and if possible, do we have some way to judge the likelyhood of it?

          • I think the best you can say is that, based on our current understanding of the laws of physics, it appears to be not just an impossible, but a meaningless excersize to try and ask the question "Is it the same particle?" At a quantum mechanical level, you don't have particles at all, you just have wave functions.

            Of course, that's not to say that our current understanding of the laws of physics is not inaccurate, so we can't say for certain that the question really is meaningless, just that to the best of our knowledge it is.
          • I suppose that particles are very close to mathematical concept of numbers. You can say that the ones in 4+1=5 and 5+1=6 are different,they are in diffrernt equations, but to distinguish between the ones in 1+1+1+1=2+2 is a complete mathematical nonsense.

            There are only 2 possibilities here: 1.the universe has a finite basic structure (which means that the universe has an underlying mathematical structure) and 2. it doesn't and it is kept together by the will of god, magic, an infinitely descending ladder of turtles or an infinite number of basic laws.

            If it's 1 (which I believe it is -- it's a hunch -- not a certitude) then the fact that fundamental particles are very close to a platonic ideal (they're all identical) should be no surprise. They're (almost) the basic bricks of the Universe and like 1s,2s and 3s they're identical.

            If it's number 2 then all bets are off.

            Anyway most/all scientists believe it's number one.

            As a side note, I also believe (call it a hunch) 1.The universe doesn't know how to count (no Godel axioms).
            2. Equational decriptions are fit for complex approximating systems. They might not be fit to describe the discrete time evolution of a discrete Universe.
            3. There are extra dimensions. Anything > 6. Some of them might be quite sizeable (have effect at microscopic/molecular/atomic scale interactions) Random results of various interactions can be simulated easily by building 1-d cellular automaton another xtra small dimension.
            4. The Universe might be quasi-static after all.
            5. There's no such thing as a black hole. They're a side effect of equational physics.

    • Re:The question is... (Score:5, Funny)

      by NoNeeeed ( 157503 ) <slash@paulle a d e r . c o .uk> on Friday July 05, 2002 @09:42AM (#3827058)
      Why does the dot keep posting stories about obviously-misinterpreted science news while ignoring *serious* news like the cure for 1/3 of cancers in mice from a week ago?

      Because not many mice read slashdot?
      • Also you already have a very good chance of recovery if you are a mouse with cancer. If one tenth of miracle cancer cures for mice worked for humans, cancer would have been a long lost illness.
    • while ignoring *serious* news like the cure for 1/3 of cancers in mice

      Hey moderators!!!! Wake up, what do you think will kill us geeks off... Cancer... Monitors, cellphones, wireless all give off radiation, some to lesser degrees, but all contribute to the problem.

      Cancer is very relevant, as right now I have a lead belt over my boys to protect them :)

    • I didn't see any science news on the dot (http://dot.kde.org [kde.org]) lately.

      /. is not the dot. The dot is the dot, and always has been.

    • "While I'm ranting: Why does the dot keep posting stories about obviously-misinterpreted science news while ignoring *serious* news like the cure for 1/3 of cancers in mice from a week ago?"

      I have another question... What's the point of linking to an article when the /. "blurb" contains practically the entire contents of the piece anyway?

      from the Cut-and-Paste-Reporting dept.

      Yeesh.

      • What's the point of linking to an article when the /. "blurb" contains practically the entire contents of the piece anyway?

        To lend journalistic integrity to those "blurb"s, I would guess. ;-)

    • Even the cure for 1/3 of cancers in mice is old news, as anybody that knows anything is aware that Canadian reasearchers discovered the definitive cause for cancer almost a decade ago... that being, Bruce McCulloch.

  • Errrr. I dont buy it. (Score:2, Interesting)

    by CDWert ( 450988 )
    "sometimes appears to leave before they enter"

    Does this mean all those magicians are correct when they say the hand is tuly quicker than the eye ?

    Seriously are they even close to certain that their detection methods are accurate or is this a side effect of the enviroment on the detection equiptment. Wouldnt be the first time.
  • You know, I'd be surprised if more than a couple of /. readers actually understand that paper. I just read it, and its pretty hard core. Well over my head.

    Amazing what gets posted on /. Then again, no-one actually reads the articles, anyway....

    Michael
    • I didn't understand 90% of the maths, and I suspect it would be impossible to do so without a maths or physics degree...but I found this section in plain english explains quite clearly what exactly is meant by particles leaving before they arrive:

      At low k values, we observe that t becomes negative over a rather wide range. For wavepackets with momentum components mainly in this range, a peak in the transmitted wavepacket can appear before the peak of the incident wavepacket has reached the condensate. This is confirmrmed by wavepacket simulations.

      So it's about the peaks of waves rather than actual particles, which makes more sense.
    • Scientists today discovered that when news hits a "Slashdot Medium," the news is translated into "comments" which may or may bear any relationship to the original news. These comments occasionally appear before the news is fully transmitted throught the "Slashdot Medium" but do not appear to violate causality.
    • From the article :
      It is well known that the Bogoliubov treatment leads to excited states ranging from phonon like disturbances of the mean field amplitude at low energies to particle like excitations at high enough energies.
      It says it's well known, and you imply that /. readers don't know that? (or, huh, understand what it's talking about?)
      I mean, come on, this is /. !

      We're all of us here l33t nerds!

    • Then again, no-one actually reads the articles, anyway...

      Hell no! The articles are usually dry and boring, while the posts that get modded up are either funny or interesting (or easily ignored without breaking the train of thought) and all the important points from the article can be inferred from them anyway.
    • I don't understand much of the mathematics behind the paper, but oddly enough, I worked in that field for about 9 months. The professor I worked for was one of the authors of 3 of the papers cited in the bibliography. Granted, my contribution to the project wasn't much (I built a capacitance bridge used to measure liquid helium levels and I did some data acquisition), but it was still a lot of fun.
    • Then again, no-one actually reads the articles, anyway....

      Hey, I read Playboy^H^H^H^H^H^H^Hslashdot for the articles!

  • Typical (Score:5, Funny)

    by BoBaBrain ( 215786 ) on Friday July 05, 2002 @09:00AM (#3826899)
    One minute you're striking a BEC, the next minute 10 seconds have gone by.

  • That's why Bose speakers are so expensive (Score:1, Funny)

    by Anonymous Coward
    Bose makes the best speakers, the sound comes out before it comes in.

    I get it now!

  • it's like seeing the light at the end of the tunnel before anyone in the middle does..

    this is somewhat exciting field

  • BEC? (Score:2, Funny)

    by tsa ( 15680 )
    It looks like a BEC is something like a Borg Einstein Collective from the atoms' point of view.
    • At the quantum mechanical level, everything is a Borg collective. Individual particles are irrelevent, all that matters is the collective, erm I mean the wave functions.

  • good explanation of particle/wave duality (Score:4, Informative)

    by shiafu ( 220820 ) on Friday July 05, 2002 @09:16AM (#3826955)
    Stephen Hawking explains these concepts marvellously in his book, A Brief History of Time [amazon.com]. It's an easy read, but also very informative.

  • Eureka! (Score:4, Funny)

    by Jucius Maximus ( 229128 ) on Friday July 05, 2002 @09:18AM (#3826963) Journal
    I have discovered a truly wonderful explanation of this phenomenon, which unfortunately the lameness filter will not let me post!

  • I thought I understood (Score:4, Funny)

    by looseBits ( 556537 ) on Friday July 05, 2002 @09:19AM (#3826964)

    The first time I leanerd quantum mechanics, I didn't understant it.

    The second time I learned quantum mechanics, I thought I understood it.

    The third time I learned quantum mechanics, I knew I didn't understand it.

  • Group Velocity (Score:1, Informative)

    by Anonymous Coward
    On reading the article it seems the clue lies in the group velocity. Is it then possible that speed of tunneling can exceed that of the group velocity?

    Looking closely it is not given that is a limit, though I would expect the speed of the tunnelig "transport" would be lower than that of light in vacuum, c\sub{0}.

    Is it really so simple as just making sure the group velocity is slow? Of course wave velocity cannot end up faster than the group, or the wave exceeeds the signal...
  • I know the discovery of the BEC won a Nobel prize.

    I just wonder how many secrets studying BEC's will unlock. How many questions that can be answered.

    May it prove to be a more momentous discovery than the transistor?
  • Where the top 5 (and only) three-and-above comments are ranked as Funny. Sheesh. You'd think this was a humor website!

  • Not so new!! (Score:4, Funny)

    by elmusafir ( 590465 ) on Friday July 05, 2002 @09:49AM (#3827109)
    I remember that something similarly shocking was published back then in 1948.

    The article in question was:

    "The Endochronic Properties of Resublimated Thiotimoline"

    Let's give some credit to pioneers! ;-)

  • As an atom hits the BEC, it is absorbed into the collective state but still exists as a vibration. The vibration travels through the BEC but can escape as an atom once more.

    So basically it's a quantum Executive Toy, right? :-)
    "The Bose-Einstein Condensate Simulator" sounds much cooler that "Cats Cradle" or whatever the doohicky with the swinging ball-bearings is called.

    Peter.
  • If a time machine can exists we've already knew it.
  • ...atoms striking a BEC sometimes appears to leave before they enter...

    Can somebody point me to where in the paper this is claimed ? If it's true then what happens if you destroy the atom going in just after the atom has come out ?

  • ...What are those 5 balls on strings called?...where you lift one and
    release it and when it hits the others the last one goes up. Lift two ...
    two go up, three....three go up....etc..

    Didn't read the article but the comments all seem to reminds me of this
    ball-string device.

  • A couple of points (Score:4, Informative)

    by doru ( 541245 ) on Friday July 05, 2002 @10:23AM (#3827286) Homepage
    First of all, this is a theoretical paper, they do not detect anything.

    Second, there's no "magic" in it. As they say in the article, the peak of the transmitted wavepacket appears before the peak of the incident wavepacket has reached the condensate.

    At the beginning of the century (1914), Brillouin and Sommerfeld already showed that, when a plane EM wave with a sharp forward front propagating in vacuum is incident upon a transparent medium, its shape is changed and precursor waves form, with a velocity approaching c in vacuum, corresponding to the high-frequency components for which the (relative) permittivity goes to 1.

    In excitable media (and I assume the same happens with atoms in a BEC) the effect is even more spectacular, because these fast components (or, as in this case, the leading edge of the pulse) can get amplified and then leave the medium before the "bulk" of the incoming pulse even enters it.

    Moreover, before leaving the medium this "fast" pulse is split in two, and the reflected component can interfere destructively with the "lazy" pulse, wiping it out. Hence the "illusion". Needless to say, Einstein is still right :-)

  • Offtopic: Moderation for difficult science stories (Score:4, Insightful)

    by The Grassy Knoll ( 112931 ) on Friday July 05, 2002 @10:40AM (#3827401)
    I haven't got the first clue about "the scattering properties of a Bose-Einstein condensate held in a finite depth well", and I doubt many people here have.

    To prove my point, most of the mod'ed up comments here have been mod'ed as 'Funny', rather than 'Interesting' or 'Informative'.

    Seems symptomatic of most hard science posts on /.

    That's it. My post-pub waffle is over.
  • Can you imagine a BEC Beowulf cluster!! ;)
  • Having read the paper (forgive me, I'm new here), I'd say the negative time effect is very similar to the FTL transmission results reported earlier. On page 6 of the paper, the caption to Figure 6 reads in part: Note the negative values of tau-sub e (the time spent inside the condensate region) in the region around ka ~/2: Wavepacket simulations show that here the peak of the transmitted wavepacket appears before the peak of the incident packet reaches the condensate. Now, IANA condensed matter physicist, but my best assessment of the effect is that it operates similarly to previously observed, similar phenomena of "FTL" transmission. The incident wave of light contains information for the entire wave embedded in the wavefront- so the peak of the wave is able to be reconstructed on the other side of the BEC, even though the peak itself has not reached the condensate yet. Essentially, since the entire wave of light is defined by a wavefunction, the entire wave can be constructed from the wavefront. Although the process can take zero or even negative time, it is not a violation of general relativity. The light itself propagates at the speed of light, as it must. Since the peak of the wavepacket is recreated before it is actually destroyed, it would seem to be moving faster than the speed of light. However, the information that completely describes this peak is embedded into the wavefront, which travels at the rather pedestrian speed of light (and for a BEC, it is almost pedestrian- the amazing dispersive effects have been shown to reduce c to around 38 miles per hour, an effective refractive index of over 17 million!). While something is technically traveling over a nonzero distance in zero or even subzero time, no unique information can be transmitted in this manner- since the peak is constructed from information in the wavefront, the peak must be composed of information contained in the wavefront. The wavefront is moving at the speed of light, and taking all of the information it has with it at exactly that speed. If we had an ultrafast and ultrasmall computer conceivably, we could dispense with the Bose-Einstein condensate and do this thing ourselves. The wavefront enters a detector, the information is broken down, and the hypothetical supercomputer we have at our disposal uses the information in the wavefront to calculate the wavefunction. It then spits out a wavepacket with characteristics identical to those of the incident packet, and does so before the peak of the incident packet even reaches the detector. The effect is somewhat analogous to the movement of lights on a scrolling theatre marquee. The scrolling itself can actually occur faster than the speed of light, but since the "information" is just a discrete on/off light, no useful FTL message can be encoded. In the same way, the wavefront carries information faster than the speed of light, but the information merely codes for the rest of the wavepacket! Thus, it is not a violation of relativity. If anything, it is an affirmation- the weirdness of quantum mechanics, what with the wave/particle nature of light, is weird in such a way that useful messages cannot be sent faster than the speed of light. On a completely different note, I was amused to see someone referenced in this paper that /.ers might recognize, if they had actually read the paper. On page 6, the authors propose explanations for this effect, and they suggest a many-body interference mechanism devised by Ray Chiao et al. Raymond Chiao, some of you may remember, is the physicist who had a /. story not long ago about the possibility of a gravitational Meisser effect for superconductors (Can Superconductors Block Gravitational Fields?).
  • Allen Varney writes "According to a story on EurekAlert, an arXiv preprint server paper titled 'Scattering of atoms on a Bose-Einstein Condensate' reports that atoms striking a BEC sometimes appears to leave before they enter.

    Umm, If you actually read the article you'd find out that it was a theoreical study, a prediction, rather then an actual observation.

    Actual observations of this mathematicaly predicted phenomonen have yet to occur.

    The science was WAY out of the league for 99% of all /. users - myself included - fortunately I understood the first paragraph :)

    Bad /. article - NO Doughnut :(

  • This story isn't really as sensational as it's made out to be. Read the paper a bit, and you'll find, right near the conclusion, this:
    Negative transmission times is a wave phenomenon, which together with superluminal propagation
    has been observed for light propagation through wave guides and through dispersive atomic media. It is not suprising that the [equations we used] show similar effects, and, indeed, Ray Chiao et. al. [ref] have suggested a [...] mechanism. [...] From our [...] analysis it is not clear whether it is due to this mechanism or if it is more closely related to the time delays which may also be observed in normal wave packet tunneling through barriers
    (emphasis mine)

    This is a phenomenon that has been observed in other places already, either through quantum tunneling [byu.edu] or through some similar quantum effect suggested by the group (Chiao et. al.) mentioned in the article. The (non-sensational) news is that it occurs in BEC's as well.

    BMagneton

  • Not mysterious - here is an explanation (Score:4, Interesting)

    by Anonymous Coward on Friday July 05, 2002 @12:57PM (#3828164)
    This seems deep and mysterious, but it is just a trick. To understand the trick you just need to understand two terms and one concept.

    Here is the first term. If you change something, your change will cause changes to propagate outwards. That rate is called the group velocity. This is the rate at which changes propagate, and cannot exceed the speed of light (thanks to Einstein).

    Here is the second term. If you sit and watch the waves go by, the peaks of the waves have an apparent motion. That rate of motion is called the phase velocity. The phase velocity is the most easily measured apparent motion.

    Here is the concept. After you have been sending a constant stream of waves for a while, the phase and group velocities have nothing to do with each other! In particular this paper just says that the phase velocity can be made negative, that is the waves look like they are moving backwards. Mildly amusing, but commonplace.

    If you want to visualize this, draw a 2 vertical lines on a piece of paper. Those lines are light-weight plastic barriers. On either side you have water, and inside you have something else - oil say. Visualize a stream of waves coming from right to left. They hit the first barrier, part bounces, part goes in. They hit the second barrier, most bounces, part goes out. The part that bounces from the second to the first, well most bounces, part goes through. And back and forth we go.

    The incoming wave train sets up a resonance in the middle third. Depending on the details of that resonance, the waves in the middle section may move forward, stand still (if you do it just right) or even go backwards. When they go backwards, ohmigosh, the wave is leaving before it goes in, we have waves moving backwards in time!

    Amazing, isn't it? And isn't it astounding that when you stop the waves coming in, between the two barriers your waves keep on bouncing back and forth for a while, and most emphatically the stoppage does not arrive on the other side before you stopped?

    Cheers,
    Ben

  • Not so spectacular (by original author) (Score:2, Interesting)

    by Anonymous Coward
    I was quite surprised to see our paper on /. Please note, that the mentioning of negative transmission times is aimed at an audience who will not see this as a very spectacular thing. Hopefully fascinating, but not sensational!
    Concepts like faster-than-light tend to draw a lot of attention from the general public (well, at least part of it :) ). Whether this is a good thing for physics is not clear to me: Will it help recruitment of new students? Or will they be turned off and go and do "useful things"?

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